The present invention is directed to a hot gas generation system for producing combustible gases which can be burned for heating boiler water or other thermo-fluids such as oil to be circulated through heating systems in plants and the like, or which can be used in the production of electrical power, or to furnish steam for various industrial and commercial purposes such as lumber drying, canning, and many other purposes. Various prior art gasifiers for burning high moisture content, organic biomass materials such as wood chips and garbage have been proposed, and are illustrated in a number of the following prior patents:
______________________________________ 3,818,848 Gardner 3,999,744 Kotch 4,184,436 Palm et al 4,300,456 Messersmith 4,308,034 Hoang 4,388,082 Guttmann et al 4,424,755 Caffyn et al 4,480,557 Hochmuth 4,583,992 Rogers 4,601,730 McGowan et al 4,627,367 Butt 4,691,846 Cordell et al 4,716,842 Williams 4,747,355 van Berkum 4,803,836 Blanton et al 4,900,401 Horton 4,947,769 Whitfield 4,971,599 Cordell et al 1,846,477 D. Dreier 4,465,022 Virr 4,593,629 Pedersen et al 4,531,462 Payne 2,088,679 K. Yamazaki et al 1,888,585 W. B. Chapman ______________________________________
U.S. Pat. No. 2,088,679 discloses a system in which fuel is supplied into the bottom of a gasifying retort surrounded by a grate, and combustible gases are recirculated through the retort to enhance the oxidation of the fuel bed. U.S. Pat. Nos. 4,691,846 and 4,971,599 disclose a similar gas generation system for producing gases for boiler water heating purposes. In this system, combustible gases are said to be recirculated back down through the mass of burning material to enhance the combustion thereof.
One of the prime objects of the present invention is, in contrast, to avoid the recirculation of gases through the bed or mass of biomass material and to direct the gases given off instead to a secondary heating chamber without combusting more than enough of them in the primary chamber to maintain the desired temperature in the primary heating chamber. The present invention seeks to minimize the non-useful combustion of gases produced by incompletely combusting biomass material in the bed and instead seeks to maximize gas production by the bed. In the applicants' system, incomplete combustion in the central portions of the bed interior produces large volumes of burnable gases, while complete combustion occurs only at the exterior surface portions of the bed and at the perimetral portions of the bed to reduce the remaining carbons in these portions to ash.
Other patents, such as Caffyn et al U.S. Pat. No. 4,424,755, in a different incineration process, also pass the gases of combustion to a secondary chamber wherein there is a separation of particulate matter from the gases. While the present system also uses a cyclone-type secondary heating chamber, it seeks to combust the fly ash particulates entrained in the gases in a secondary cyclone chamber having walls heated sufficiently to combust the particulates, without undue burning of the combustible gases from which they are separated.
The Whitfield U.S. Pat. No. 4,947,769 discloses a system for the combustion of solid particulate fuel which utilizes a perforate fire table. The table is supplied with fuel from above and employs a rotating member above the grate to remove ash and clinkers from the grate.
The Butt U.S. Pat. No. 4,627,367, is directed to a coal-burning, gas generating apparatus in which fuel from above is supplied to a coal bed which is fluidized due to the supply of air under considerable pressure to the lower end of the coal bed. In contrast, the present invention seeks to avoid the fluidization of the mound-like bed, while furnishing greater volumes of air to the central portion of the bed than to the perimeter thereof.